1. Field of the Invention
The field of the invention relates to metering pumps for pumping relatively precise volumes of fluid.
2. Brief Description of the Prior Art
Valveless, positive displacement metering pumps have been successfully employed in many applications where safe and accurate handling of fluids is required. The valveless pumping function is accomplished by the synchronous rotation and reciprocation of a piston in a precisely mated cylinder bore. One pressure and one suction stroke are completed per cycle. A duct (flat portion) on the piston connects a pair of cylinder ports alternately with the pumping chamber, i.e. one port on the pressure portion of the pumping cycle and the other on the suction cycle. The mechanically precise, free of random closure variation valving is performed by the piston duct motion. A pump head module containing the piston and cylinder is mounted in a manner that permits it to be swiveled angularly with respect to the rotating drive member. The degree of angle controls stroke length and in turn flow rate. The direction of the angle controls flow direction. This type of pump has been found to perform accurate transfers of both gaseous and liquid fluids.
The manner in which the pump head module is swiveled with respect to the drive member varies among the different available metering pumps. In one commercially available pump, the pump head module is secured to a plate which is, in turn, mounted to the base of the pump. The plate is pivotable about one of two pivot axes depending upon the angular orientation of the module. The base may be provided with graduations to indicate the percentage of the maximum flow rate achieved at the particular angle at which the module is directed. The maximum flow rate is achieved when the module is at its maximum angle with respect to the axis of the rotating drive member.
A valveless positive displacement pump including a working chamber which is angularly displaceable with respect to the axis of a drive shaft is disclosed in U.S. Pat. No. 4,008,003.